The present invention relates to a heating apparatus for heating a substrate to be treated, and in particular to a heating apparatus suitable for heating a resist pattern before or after exposure in photolithography or the like, a method for evaluating a heating apparatus and a pattern forming method.
Conventionally, a photolithography has been used to form a circuit pattern on a semiconductor apparatus. In the photolithography, heating process (bake) is performed on a resist before or after exposure. Regarding heating a semiconductor wafer (substrate to be treated) before or after exposure, the amount of heat supplied to the semiconductor wafer form a heating plate during heating process has conventionally thought to be constant, and the heating amount has been determined by effecting heating for a constant time period.
In such a method for controlling the heating amount, however, there is a problem that, since a temperature profile during heating is different for each wafer, the heating amount is actually different for each wafer. Also, as the temperature of a wafer can not be measured when there is a temperature distribution in the surface of the wafer, the temperature distribution in the intra-wafer can not be made uniform.
For this reason, when such a resist is used that its pattern dimension changes largely according to the heating amount, variations in dimension have occur on the intra-wafer and the inter-wafer. Furthermore, in the temperature measuring which has been conventionally performed with infrared light, it is the existing situation that, since the infrared light is longer in wavelength than visual light or ultraviolet light, a sufficient accuracy can not be obtained when optical change is monitored using the infrared light.
Also, in order to control a dimension of a resist pattern of intra-wafer with a high accuracy, it is important to control the treating temperature of a semiconductor substrate during heating uniformly and accurately. Specifically, in a lithography step, a temperature uniformity for a bake process after exposure, called PEB (Post Exposure Bake), is regarded as important due to introduction of a chemically amplifying type resist.
In order to attain an intra-wafer uniformity with a high accuracy, it becomes important to measure the surface temperature of a substrate during heating process in its surface accurately to control a heating apparatus.
As one method for measuring the surface temperature of a substrate during heat treatment, such a method is given that a product where such a temperature sensor as thermocouple is embedded in the same substrate as a substrate to be subjected to heat treatment, for example Process Probe 1840 type manufactured by SensArray COP. is heat-treated to be used for a temperature measurement. However, when the bake process is performed in a sealed space in order to take out wires connecting the sensor which has been embedded in the treated substrate and a measuring unit from the bake unit, since the wire injures the sealing condition, it is difficult to reproduce the conditions of the processing time at a time of temperature measurement as it is, thereby lacking measuring accuracy. Also, as conditions such as a position where the substrate is disposed or the like can not be reproduced at the time of temperature measurement, there is a problem that a reliability of the measured result is injured.
Furthermore, when a bake process is effected in a state where such volatile material as solvent is included, a processing container (chamber) is generally exhausted and/or purged by such inert gas as air or nitrogen to form wind flow in the chamber in order to prevent the volatile material from attaching to the processing chamber. When a temperature measurement is conducted by an apparatus where a sensor is embedded in a substrate, the wind flow is disturbed by the wire which has been drawn out, which means that a temperature measurement is performed in a state different from the actual processing state, thereby resulting in a factor deteriorating the measuring accuracy. Also, there is a problem that a temperature lowering due to the exhaust wind can not be measured accurately due to a sealing resin for fixing the sensor.
In order to solve this problem, there has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 11-8180 a method where the surface temperature of a substrate during the bake process is measured over its entire region by an infrared sensor (an infrared thermography process) which has been assembled in a bake unit and temperature control of respective divided heaters is performed on the basis of the temperature distribution information obtained. However, there is a problem that a sufficient measuring accuracy can not be obtained since the value of the temperature measured using the infrared temperature sensor largely depends on a film structure of film thickness of a substrate. There is also a problem that, since an infrared temperature sensor with a high accuracy which can measure a substrate over its entire surface is very expensive in general, the cost for manufacturing the bake unit is increased so that the back unit is impractical.
Meanwhile, there has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 10-275755 a method and an apparatus where the line width of a latent image (an exposed portion/an unexposed portion) after PEB is measured and the measured result is fed back to the PEB temperature condition. In this method, however, there is a merit that no expensive measuring equipment is mounted on the bake unit, but there has occurred a problem that, as the resist latent image does not be made rectangular, it is difficult to measure the line width of the latent image and it is also difficult to feed back the measured result to the PEB temperature condition with a high accuracy.
Also, it is generally difficult to expose an intra-wafer with the completely same exposing amount and variations among respective shots occur. For this reason, it is necessary to uniform the temperature distribution and simultaneously to uniform a distribution of exposing amount actually incident on a resist in order to suppress the variations in dimension. However, it has been impossible to measure the temperature distribution and the actual irradiated exposing amount accurately.
Thus, there has conventionally a problem that, when the heating process is performed before or after exposure on the substrate to be treated on which a resist has been applied, it is impossible to accurately measure the heating amount of the substrate to be treated, to that variations occur in dimension.
Also, the heating temperature of the substrate to be treated can accurately be measured during the heating process so that it is impossible to evaluate a heating apparatus. Also, as the heating temperature can accurately be measured, there is a problem that the heating apparatus can not be controlled so that evenness of the heating temperature occurs in the intra-substrate and variations occurs in dimension of the resist pattern.
Also, there is a problem that the temperature distribution and the distribution of exposing amount of light which has been irradiated actually can accurately not be measured so that an exposing apparatus and the heating apparatus can not be evaluated. Furthermore, there is a problem that since the actual exposing amount and heating temperature can not be measured accurately so that the exposing apparatus and the heating apparatus can not be controlled, thereby resulting in that variations occur in dimension of the resist pattern.